Protons Greatly Influence the Properties of the Neutron Stars

August 15, 2018

The findings of CLAS Collaboration might alter the understanding of people about neutron stars.

It is quite obvious from their name that neutron stars are comprised primarily of the neutral subatomic particles known as the neutrons. Due to this reason, it was assumed that most of the properties of the neutron stars are influenced by neutrons but a recent study has presented an entirely different idea to the world. According to the researchers of the MIT, a smaller fraction of protons (around 5%) have an incredible impact on their properties. These claims were backed up by a detailed analysis of the microscopic nuclei of atoms on Earth.

It is a well-known fact in the scientific community that the nucleus of an atom is packed with protons and neutrons. These subatomic particles can indulge in ‘short-range correlations’, where a proton pair with a neutron to streak through the nucleus of an atom with extremely high energy. These correlations have a significant effect on the overall properties of the given atom. For sake of their experiments, the researching team examined the atoms of Carbon, Iron, Aluminum, and Lead. All of them have a higher ratio of neutrons to protons.

It was observed that there is a direct relationship between the number of neutrons and the chances of a proton forming an energetic pair. The chances of a neutron forming a pair remained the same in each element. Therefore, the researchers concluded that the minority of protons carry most part of the average energy in the objects having large densities of neutrons. Or Hen, an Assistant Professor of Physics at the MIT, mentioned that by saying,

“We think that when you have a neutron-rich nucleus, on average, the protons move faster than the neutrons, so in some sense, protons carry the action. We can only imagine what might happen in even more neutron-dense objects like neutron stars. Even though protons are the minority in the star, we think the minority rules. Protons seem to be very active, and we think they might determine several properties of the star.”

The data collected by CLAS – the CEBAF (Continuous Electron Beam Accelerator Facility) Large Acceptance Spectrometer was used for this analysis. It was originally designed to detect and record the multiple particles that are emitted when beams of electrons are directed towards atomic targets. It kept working for 14 years from 1998 to 2012 at the Jefferson Laboratory. The researching team was inclined to use the data from CLAS because it did record the short-range interactions as well although it was not a part of its job description. Larry Weinstein, the Collaborator of the study who is a Professor of Physics at the Old Dominion University, said,

“People were using the detector to look at specific interactions, but meanwhile, it also measured in parallel a bunch of other reactions that took place. So we thought, ‘Let’s dig into this data and see if there’s anything interesting there.’ We want to squeeze as much science as we can out of experiments that have already run.”

In 2004, an experiment was performed in which electronic beams were bombarded on the atoms of Carbon, Aluminum, Iron, and Lead to observe the movement of produced particles in a larger volume of each element. The researchers wanted to see whether the probability of pairing, changes with the ratio of neutrons to protons or not. A total of 182 members from different institutions of 9 countries were a part of this team which is known as the ‘CLAS Collaboration’. Hen talked about their intentions in the following words:

“We wanted to start from a symmetric nucleus and see, as we add more neutrons, how things evolve. We would never get to the symmetries of neutron stars here on Earth, but we could at least see some trend and understand from that, what could be going on in the star.”

The results showed that the probability of protons making pairs increased significantly with the increase in a number of neutrons in the nucleus of an atom. Following this trend, Hen mentioned that the role of protons will be even more significant in denser objects like neutrons stars. For example, it is quite possible that energized protons are determining the ratio of mass to size and the process of cooling of a neutron star. Hen said,

“All these properties then affect how two neutron stars merge together, which we think is one of the main processes in the universe that create nuclei heavier than iron, such as gold. Now that we know the small fraction of protons in the star are very highly correlated, we will have to rethink how [neutron stars] behave.”

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